Solar radiation includes about 5% ultraviolet (UV) radiation, wavelength of which is between 200 nm and 400 nm. It is further classified into three regions: from 320 to 400 nm (UV-A), 290 to 320 nm (UV-B) and from 200 to 290 nm (UV-C). A large part of UV-C radiation is absorbed by the ozone layer. Scientific studies have indicated that exposure to UV-A and UV-B radiation for short period causes reddening of the skin and localized irritation, whereas continued and prolonged exposure can lead to sunburn, melanoma and formation of wrinkles. It is also reported that UV radiation causes significant damage to hair. Therefore, it is desirable to protect the skin and other keratinous substrates of the human body from the harmful effects of both, UV-A and UV-B radiation.
Various cosmetic preparations have been reported for preventing and/or protecting the skin from harmful effects of ultraviolet radiation. Numerous organic sunscreen agents capable of absorbing UV-A rays are reported in the field of cosmetics. Many UV-B sunscreens are also known and approved for safe use in personal care compositions for protection from UV-B radiation.
Inorganic sunscreens, also known as inorganic sun-blocks, are also used in photoprotective compositions. They work by blocking out the rays of the sun, no matter what the wavelength. They are included in such compositions in carefully calculated amounts and in carefully determined particles sizes. This is necessary since a choice of the wrong particle size or amount leads to either poor sensories on application of the composition on the skin or an unnatural whitish appearance when applied on the skin. Commonly used inorganic particles are zinc oxide, iron oxide, silica, mica, titanium dioxide or coloured pigment particles.
Cosmetic compositions are formulated in various cosmetically acceptable vehicles (or bases) depending on the sensory properties desired. Compositions may be formulated in an anhydrous vehicle or a water containing vehicle. Compositions comprising water may be formulated as a gel or as an emulsion. Gels are generally compositions comprising predominantly water with minimal or no oily phase. Composition comprising both water and oily phase are formulated as emulsions which may be an oil-in-water emulsion or a water-in-oil emulsion. The difference between these two types of emulsion is that although the ranges of water and oil overlap, the difference is in whether water is the dispersed phase or the continuous phase and vice-versa. The present invention relates to a water containing composition in the form of a oil-in-water emulsion which comprises fatty acid or an ester thereof and a cross-linked acrylic acid polymer. This type of a composition gives an emulsion in a lamellar phase. When such compositions are rubbed on to the skin they give a watery sensation which are liked by many consumers. When such compositions are to be formulated for sunscreen benefits, by including inorganic particles in them, they tend to cause an inordinate increase in the viscosity of the compositions. Concomitantly they affect the tactile sensory appeal of the compositions when they are rubbed on to skin. It is thus a problem to incorporate even small amounts of inorganic particles in such compositions without affecting the sensory appeal. The present inventors have, through extensive experimentation determined that inclusion of hydrophobic polymer particles of a specified particle size range enables such compositions to not only provide the sunscreen benefits but also deliver the excellent watery sensation the consumers have come to expect from such compositions.
US2008242573 (Procter & Gamble) relates to a multiphase personal care composition which comprises an aqueous structured surfactant phase, a structuring system, and a benefit phase. The aqueous structured surfactant phase comprises from about 5 percent to about 16 percent, by weight of the multiphase personal care composition, of a lathering surfactant selected from the group consisting of anionic surfactants, nonionic surfactants, amphoteric surfactants, cationic surfactants or mixtures thereof and a structuring system. The structuring system comprises a non-ionic emulsifier having an HLB of from about 1.4 to about 13 by weight of the multiphase personal care composition, of an associative polymer; and an electrolyte. The benefit phase comprises from about 5 percent to about 30 percent, by weight of the multiphase personal care composition, of hydrophobic benefit material. The present invention differs from this published document in that this publication discloses that fatty acid is not included in such compositions. Therefore it can be inferred that such compositions do not deliver the sensory properties expected from such compositions.
It is thus an object of the present invention to provide for sunscreen compositions that exhibit the consumer preferred watery sensation from such compositions comprising a fatty acid or a ester thereof and a cross-linked acrylic acid polymer.